Is it possible to create realtime outline effect in Eevee, only with shaders?
Here's a rough attempt in eevee.

A Shader to RGB and a color ramp in constant mode, with a limited range of colors, then used for color in an other diffuse shader, will take care of the toon look.
Fresnel used as fac to mix a black diffuse shader will create the outline (I added a color ramp to distort the Fresnel info a bit).